Development of porous chitosan/tripolyphosphate scaffolds with tunable uncross-linking primary amine content for bone tissue engineering.

The primary amine along the chitosan backbone plays a key role in biomedical applications. Although chitosan-based porous scaffolds have been widely used in tissue engineering, it remains very challenging to regulate uncross-linking primary amine content (CN) in scaffolds in order to realize particular mechanical and biological properties. In the present study, chitosan/tripolyphosphate (TPP) scaffolds with controlled CN (i.e., degree of cross-linking) were prepared based on the ionic-dependent solubility of chitosan together with the freezing process. The effects of the concentration of TPP (CTPP) and NaCl (CNaCl) in the cross-linking solution on CN were studied by infrared spectroscopy, ninhydrin assays and elemental analysis. The results showed that CN decreased with increasing CTPP and decreasing CNaCl. CN affected physicomechanical properties such as swelling behavior and the mechanical strength of the chitosan/TPP scaffolds. The uncross-linking primary amine in scaffolds can be used for chemical and biological modifications. The protein loading of the scaffolds demonstrated that the pH-responsive adsorption and release behavior was influenced by CN. Cell experiments also illustrated that CN affected the proliferation of bone marrow mesenchymal stem cells (BM-MSCs). All of these results indicate that these porous chitosan/TPP scaffolds containing uncross-linking primary amines are potentially useful for applications in regenerative bone medicine.